Generally when a tooth is broken off or missing a bridge can be applied to replace that tooth. Similarly, a crown can be formed over a partially damaged tooth. The bridge or crown which is often called an appliance is carefully formed by a dentist to match the existing teeth of the patient. The appliance is generally made of material such as gold substrate which gives the bridge or crown structural support. Coating the surface of the appliance is a hard material such as porcelain which gives the appliance the color of the patient's natural teeth. The substrate and the porcelain are biologically non-reactive to the body.
In order to fit the appliance to the broken tooth or adjacent teeth in the case of a missing tooth, the tooth or teeth must be trimmed to the gum line. The appliance is then fitted over the trimmed region thereby filling the gap resulting from the broken or missing tooth. The appliance is attached to the trimmed region by a cement such as zinc oxide.
A problem that often occurs is that a tooth under the bridge or crown must sometimes be repaired. To enable access to the underlying tooth, the appliance must be removed. To remove the appliance, an impulse force must be applied to the cement to break the bond without damaging the underlying tooth, the periodontal tissues, or the appliance. If the appliance is damaged or broken then a new bridge or crown must be formed to replace the original, thus, resulting in a very expensive procedure for the patient.
Several methods are used to date for removing the appliance when repair to the underlying tooth is needed. Many of these methods are recited in Review of Methods for Removing Cast Gold Restorations by Richard A. Olivia, DDS, JADA, Vol. 99, November 1979. One of these methods is to use a hook device such as a reverse mallet at the edge of the appliance and apply an impulse force. One problem with employing this method is that you can chip the porcelain coating and damage the appliance. Another problem is that you can put a bending moment into the underlying tooth, causing the tooth, which has been weakened as a result of the trimming, to break off, thus, causing obvious pain to the patient.
In the case of a permanently cemented bridge, the general operation procedure is to take a saw and split the side of the appliance along the marginal side and along the crown. Once a split has been made, a small wedge is used to split open the appliance. The problem with this procedure is that the entire bridge is ruined. Additionally, there is a risk that the saw may cut into the underlying tooth and that the shock force applied by the wedge to the appliance will cause damage to the weakened tooth.
Another method employed by dentists is the Richwil crown remover device which is a gum-like device. To use the device, the gum is heated and applied to patient by placing it on the appliance and having the patient bite down. The gum device forms around and sticks to the crown or bridge and the opposing teeth. The dentist then requests the patient to separate his jaws thereby breaking the bond. The problem with this method is that often times the patient cannot develop sufficient force to break the bond. Also, cements which are commonly used by dentists require an impulse force to break the bond i.e., a constantly applied force will not break the bond.
There is, therefore, a need to remove a crown or bridge from dental patients without causing damage to the appliance or trauma to the tooth.